Most women cannot get pregnant naturally after age 45, though the biological endpoint is menopause, which occurs at an average age of 51 in the United States. Fertility doesn’t switch off like a light, though. It declines gradually over roughly two decades, with several key inflection points along the way.
How Fertility Changes Through Your 30s and 40s
Women are born with all the eggs they’ll ever have, and the supply drops steadily from that point forward. The decline is slow at first but accelerates twice: once around age 32, and again more sharply around age 37. By age 37, roughly 25,000 eggs remain in the ovaries. By 40, most women have less than 10% of their original egg supply. At menopause, fewer than 100 eggs are left.
It’s not just the number of eggs that matters. Egg quality also drops with age, which means a higher proportion of eggs carry chromosomal errors that prevent a healthy pregnancy. Hormonal markers of fertility begin shifting as early as 25, when the hormone that reflects remaining egg supply starts its long, steady decline.
In practical terms, a healthy 30-year-old trying to conceive in any given month has a meaningfully higher chance than a 40-year-old. By the early to mid-40s, natural conception becomes unlikely for most women, and by 45, the odds are very low.
Perimenopause: The Gray Zone
The years leading up to menopause, called perimenopause, typically begin in a woman’s mid-40s but can start earlier. During this phase, periods become irregular, cycles get longer, and ovulation becomes unpredictable. In late perimenopause, more than 60% of cycles don’t involve ovulation at all.
But “unpredictable” is the key word. Even in late perimenopause, about one quarter of very long cycles (60 days or more) still include ovulation. Researchers have described the risk of conception during this stage as “far from negligible.” This is why unintended pregnancies still happen in the mid-to-late 40s. You’re not considered post-menopausal, and therefore reliably unable to conceive, until you’ve gone a full 12 months without a period.
What the Numbers Look Like With IVF
Fertility treatments can extend the window somewhat, but they can’t fully overcome age-related decline when a woman uses her own eggs. IVF live birth rates using a woman’s own eggs tell the story clearly:
- Ages 41 to 42: roughly 11 to 12.5% live birth rate per cycle
- Age 43: about 9.6% per cycle
- Age 44: about 3.6% per cycle
- Age 45 and older: essentially 0% in studied programs
Donor eggs change the picture entirely. Because the eggs come from a younger woman, the recipient’s age matters much less. Pregnancy rates with donor eggs hold steady at around 30% per transfer cycle regardless of whether the recipient is 40, 47, or older. In donor egg programs, women have successfully carried pregnancies into their mid-50s. Many fertility clinics do set upper age limits for these procedures, but the limits vary by program and are based more on the health risks of pregnancy than on the ability to carry one.
Health Risks of Pregnancy After 40
Even when conception is possible, pregnancy at 40 and beyond carries higher medical risks. Compared to younger women, those over 40 are about 2.5 times more likely to develop preeclampsia (dangerously high blood pressure during pregnancy) and roughly 2.5 times more likely to develop gestational diabetes. These aren’t rare complications in this age group: in one large study, gestational diabetes affected 14.5% of mothers over 40, compared to 6.9% of younger mothers.
The risk of miscarriage also rises substantially, driven largely by the higher rate of chromosomal problems in older eggs. Pregnancies after 40 are more likely to require cesarean delivery and more likely to involve preterm birth. None of this means a healthy pregnancy at 40 or beyond is impossible. Many women have them. But the monitoring is closer and the stakes are higher.
The Short Answer, Age by Age
There’s no single age where pregnancy becomes impossible for every woman. Biology varies. But the general pattern is consistent: fertility is strongest in the 20s, begins declining in the early 30s, drops more steeply after 37, and becomes very unlikely by 45. Menopause, the definitive biological end of fertility, arrives at 51 on average but can happen anywhere from the early 40s to the late 50s.
If you’re in your 40s and not trying to conceive, it’s worth knowing that pregnancy is still possible until menopause is confirmed. If you are trying to conceive, the realistic window with your own eggs narrows significantly after 43, and donor eggs or embryos become the primary path for women in their mid-to-late 40s and beyond.